1. Technical Field
The present invention relates to a transmission device, an image data transmission system and a transmission method for transmitting image data.
2. Related Art
In an image forming system, in which image formation is performed based on designated image data, a controller to perform image processing to generate print image data and an image output device to output an image based on the generated image data are independent units. In this image forming system, the controller transmits image data, and the image output device receives the image data from the controller and performs image output such as printing. Accordingly, it is necessary to establish connection between the controller and the image output device by some communication method.
As the simplest communication method, parallel communication in which the number of bits corresponds to the data width of image data may be used. However, when connection between the controller and the image output device is established by use of the parallel communication, the number of connections is increased.
Accordingly, there is proposed an image forming system in which connection is established between such controller and image output device by serial communication.
By use of this serial communication, the number of connections between the controller and the image output device can be reduced. However, when the same data amount of information is transmitted, the transmission rate in the serial communication is higher in comparison with that in the parallel communication. In the image forming system in which connection is established between the controller and the image output device by serial communication, there is a high probability that an abnormality occurs in image data due to communication abnormality caused by the influence of noise or the like.
To prevent this problem, there is proposed an image transmission/reception system in which abnormality detection is performed to determine whether or not a communication abnormality has occurred between the controller and the image output device using test data having a preset pattern. In this image transmission/reception system, the test data is transmitted from the controller to the image output device by a method not interrupting image data transmission/reception and the test data received on the image output device side is checked, thereby occurrence/nonoccurrence of communication abnormality is determined.
According to the disclosed image transmission/reception system, when an abnormality is detected in the test data received on the image output device side, it is determined that some abnormality has occurred in the serial communication between the controller and the image output device, and abnormality processing such as stoppage of image output can be performed. Accordingly, the reliability of an outputted image can be increased by such abnormality detection.
However, when some abnormality occurs on the controller side or reset by software (hereinbelow, referred to as “software reset”) is performed for the sake of control, the test data stored in a register on the controller side is initialized. In this case, the test data outputted from the controller side does not correspond with the test data stored on the image output device side. As a result, the abnormality processing such as stoppage of image output is performed on the image output device side even though no communication abnormality has occurred.
To prevent such erroneous detection, a valid bit indicating validity/invalidity of test data may be added to the test data. In the image output device, when the valid bit indicates invalidity of the test data, determination of occurrence/nonoccurrence of communication abnormality is not performed. However, in this method using the valid bit, a problem may occur when software reset is performed on the controller side. For example, when the valid bit is reset after the reset of the test data, the valid bit indicates validity of the test data for some period even though the test data has been reset. In this case, there is a probability of erroneous detection as occurrence of communication abnormality in the image output device. Further, when the valid bit is reset before the reset of the test data, the erroneous detection as occurrence of communication abnormality is not made, but the communication abnormality detection using the test data is not performed. In this case, even when a communication abnormality has really occurred, detection is not performed.